1. Field of the Invention
This invention relates generally to a transmission mechanism for a motorcycle or the like and particularly to such a transmission incorporating a reverse mechanism by which the motorcycle can be move rearwardly.
2. Prior Art
A typical example of conventional transmissions for motorcycles comprises a shift drum having cam grooves formed in an outer peripheral surface thereof, and shift forks mounted on a shaft for sliding movement therealong and received at one ends respectively in the cam grooves. The other ends of the shift forks are engaged with shifters or shift collars mounted on a main shaft and a countershaft, and input and output gears are mounted on the main shaft and the countershaft, respectively. In operation, a gear shift pedal is operated to angularly move the shift drum, so that the shifters are moved by the coacting shift forks to drivingly connect the main shaft and the countershaft together through the meshed input and output gears, thereby transmitting the rotation of a crankshaft of an engine of the motorcycle to the countershaft at a selected gear ratio, the countershaft having a drive sprocket around which a drive chain extends to drive a rear wheel of the motorcycle in a well known manner.
A transmission of this type has also been employed in a motorcycle having three or four wheels, and in some cases such a transmission is provided with a reverse mechanism so that the three or four-wheeled motorcycle can be moved rearwardly. Japanese Patent Application Laid-Open (Kokai) No. 57-161340 discloses such a transmission of the type having a lock mechanism for normally preventing the transmission from being inadvertently shifted into a reverse state. In this conventional transmission, the input and output gears, the shift forks and the lock mechanism are all disposed above the shift drum, and they are spaced from one another so as not to interfere with one another. Therefore, the transmission is rather space-consuming and extends considerably from the opposite sides of a frame or a body of the motorcycle, and as a result the overall width of the motorcycle is increased.